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Common methods of CNC precision machining

For the machinery industry, the substances they most often contact are a series of parts and components. No matter which style or type, they will be familiar with and know more or less. The staff in the relevant industry know what kind of parts are used in which structure or application position. However, no matter which configuration, it needs to go through certain processing steps before it can be implemented in specific mechanical equipment. Therefore, professionals call this step precision part machining.

There are many ways to process precision parts, such as heat treatment. Part refers to a single piece that cannot be separated in machinery. It is not only the basic element of the machine, but also the basic unit in the process of mechanical manufacturing. Its manufacturing process generally does not need assembly process. Such as bearing sleeve, bearing bush, nut, crankshaft, blade, gear, cam, connecting rod body, connecting rod head, etc.

1、 Precision parts machining. It mainly includes precision turning, mirror grinding and grinding. Micro turning is carried out on a precision lathe with a finely ground single crystal diamond turning tool. The cutting thickness is only about 1 micron. It is often used to process high-precision and highly smooth parts such as spherical, aspherical and planar mirrors of non-ferrous metal materials.

2、 Precision parts processing. When the machining accuracy of precision parts is nano, or even finally atomic units (atomic lattice distance is 0.1 ~ 0.2 nm), the machining method of ultra precision parts can not adapt. It is necessary to use the machining method of special precision parts, that is, the application of chemical energy, electrochemical energy, thermal energy or electric energy to make these energy exceed the combined energy between atoms, So as to remove the adhesion, combination or lattice deformation between some atoms on the surface of the workpiece, so as to achieve the purpose of ultra precision machining. These processes include mechanochemical polishing, ion sputtering and ion implantation, electron beam exposure, laser beam processing, metal evaporation and molecular beam epitaxy.

About CNC Turniing

ken. tang@chengcg.com

How to accept CNC machining center?

How should CNC machining center conduct acceptance? The acceptance of CNC machining center directly affects the operation of equipment manufacturers. The general factory acceptance standard is to process and test the workpiece directly. In fact, after the workpiece processing test, we can basically determine that the key parts of the CNC machining center meet the standards and have no problems in normal use. However, there are still some details. We should also pay attention to the acceptance. It is better for the manufacturer to have its own acceptance process or standard, so as to better ensure the quality and subsequent use of CNC machining center.

Performance and function inspection of NC machine tools

It is mainly to check whether the moving parts and auxiliary devices of CNC machining center have abnormal phenomena and noise during start, stop and operation, and whether the lubrication system, cooling system and fans work normally.

Machine tool performance test:

Spindle performance inspection

Select low, medium and high speeds. The spindle is started five times continuously, and then shut down to check the flexibility and reliability of its action. At the same time, check whether the power display on the load meter meets the requirements.
Manual data input and input can gradually increase the spindle from low speed to the maximum allowable speed. Check whether the rotating speed is normal. Generally, the allowable error shall not exceed 10%. Check the spindle speed at the same time. Observe whether the noise, vibration and temperature rise of the main shaft are normal. After high-speed operation for 2h, the temperature rise of main shaft is 15 “C
In order to check the flexibility and reliability of spindle action, the spindle can be stopped for more than 5 times continuously.

Mechanical zero point check

The reliability check of the soft and hard limit of the vertical machining center machine tool. The soft limit is generally determined by the system parameters, and the soft limit reliability can be completed by checking the system parameters. The hard limit is determined by the travel switch set at the limit position of each feed shaft, and the reliability of the hard limit is determined by the reliability of the travel switch.
Check the reliability and accuracy of zero return by returning to the original point, and check the zero return performance of each feed shaft.

Inspection of feed shaft

Manually operate the low, medium and high-speed feeding and rapid movement of each feed shaft to check whether the movement proportion is correct, whether the movement is stable and whether there is noise.
Manual data input mode (MDI) operation can detect whether the rapid movement and feed speed are normal through goo and gol command functions.

Inspection of tool change device

Carry out tool exchange step by step manually. Check whether the actions such as grasping, loading and pulling are accurate and appropriate. During the adjustment of CNC machining center, the calibration inspection method is used for inspection. In case of error, the stroke of the manipulator, the support of the manipulator or the position of the tool magazine can be adjusted.

About CNC Turniing

ken. tang@chengcg.com

Large gantry computer gong processing

Large gantry computer gong processing is a common processing project in machinery, especially large-scale machining. There are still many technical problems in large-scale CNC processing. What requirements should be observed in terms of machining and technology?

Requirements for processing large gantry computer gongs

1、 Remove the oxide scale on the surface of the parts, and the machined surface of the parts shall be free of scratches, scratches and other defects that damage the surface of the parts. The tolerance of unmarked shape shall meet the requirements of gb1184-80, the standard tolerance of unmarked length shall be ± 0.5mm, and the casting tolerance zone shall be symmetrical with the basic standard equipment of blank.

2、 The rolling bearing of the device is allowed to be heated by oil for hot installation, and the oil temperature shall not exceed 100 ℃. Sealing filler or sealant is allowed to be used in the hydraulic system of the device, but it shall be avoided to enter the system. The parts and components entering the device must have the certificate of inspection before the device can be installed.

3、 Parts must be cleaned before installation, and there shall be no burrs, burrs, scale, rust, chips, oil, colorant, dust, etc. Before installation, recheck the main matching standards of parts, especially the interference matching standards and relevant accuracy.

4、 During the use of large gantry computer gong processing equipment, parts are not allowed to be knocked, bumped, scratched and rusted. When fastening screws, bolts and nuts, it is forbidden to use improper screwdriver and wrench for impact or use. After fastening, the screw groove, nut, screw, bolt head, etc. shall not be damaged due to large CNC processing. For fasteners that are tightened according to the specified torque requirements, a torque wrench shall be selected and tightened according to the specified tightening torque.

About CNC Turniing

ken. tang@chengcg.com

Reasons for poor machining accuracy of CNC

The precision of hardware parts almost determines the quality of products. The more precise hardware parts are, the higher the requirements for precision are. So why does the machining accuracy of precision parts become worse? Here are the answers for you:

Precision parts processing

1、 The factor is the poor machining accuracy of the part itself. Generally speaking, if the dynamic error between shafts is not adjusted well during installation, or changes due to the wear of shaft transmission chain, the accuracy of parts will be affected. Generally, the accuracy of text search caused by such errors can be adjusted to compensate for the amount of resolution. If the error is too large or even an alarm occurs, it is necessary to check the servo motor and observe whether its speed is too high.

2、 The factor is that excessive operation will also affect the machining accuracy of the machine tool. This may be because the acceleration and deceleration time is too short, and the appropriate expansion and change time. Of course, it is also very likely that the link between the lead screw and the servo motor is loose.

3、 The reason is that the roundness out of tolerance caused by the linkage of the two shafts, the axial deformation of the circle formed by the machinery is not adjusted properly, the lead screw clearance compensation of the shaft is not correct, or the shaft positioning is offset, which may affect the accuracy of precision parts.

About CNC Turniing

ken. tang@chengcg.com

Application method of CNC fast wire cutting

For the current processing industry, wire cutting is a very common cutting process. For fast cutting wire cutting, the same mechanical equipment will have certain differences in product quality after being operated in the hands of different people, which will also have a certain impact on the normal use of machine tools. Here, the methods for fast wire cutting will be briefly introduced. First, find the line you are cutting.

The line method is correct. If you are working on a multi-layer thin-walled sheet metal part because it will be affected by dimensions such as welding or blanking, the edges of the plate will not be neat. At this time, if the cutting accuracy is not high. In this case, it can be done by using the chemical fiber arrangement method or by manual method.

The alignment method of paper pattern is also a common method. When the multi-layer thin-walled bow and arrow is used for cutting shape processing, the inner contour or hole must be operated. Then, it is necessary to carry out silk pre threading in multiple places. At this time, we can paste one-to-one paper pattern on the workpiece to be processed, which will not only lead to the deviation of wire hole, but also lead to wire cutting. It will also become easier. Rapid cutting wire cutting is also a technology for cutting internal control, keyway or outer circle, which makes it possible to cut tooth shaped workpiece.

For the process hole to be corrected, many workpieces should be processed according to the machining steps. Generally, this process shall be carried out on the left and right sides of the plate and at the diagonal. At this time, the size or surface quality of the machined hole is a better case. You can use the corresponding hole on the bridge tool, and then use the position of the tip to perform alignment.

Universal table alignment is also a common alignment method using rapid cutting line cutting technology. The most important feature of this correction method is that the accuracy is relatively high, so the probability of using it is relatively large. Rapid cutting line is one of the cutting methods used at present. This cutting method requires higher cutting technology, but the cutting technology is actually based on cutting experience, so for the operator, we must accumulate some experience.

About CNC Turniing

ken. tang@chengcg.com

What is the usual speed of CNC machine tools

With the improvement of the performance of the core processor of CNC system, the feed speed limit of high-speed machining center can reach 80m / min and the empty running speed can reach about 100m / min. At present, many automobile factories in the world, including China’s Shanghai General Motors Company, have adopted the production line composed of high-speed machining centers to partially replace the modular machine tools. The feeding speed limit of the hypermach machine tool of Cincinnati is 60m / min, the fast speed is 100M / min, the acceleration is 2G, and the spindle speed has reached 60000r / min. It takes only 30min to process a thin-walled aircraft part, while the same part takes 3 hours in general high-speed milling machine and 8 hours in general milling machine. Due to the specialization of the division of labor among the components of the mechanism, the high-speed spindle is becoming more and more popular with the development of professional spindle factories. In the past, the models used only for High-speed Automobile Industry (models with more than 15000 revolutions per minute) have become an essential element of mechanical products.

About CNC Turniing

ken. tang@chengcg.com

How to select hard rail processing and wire rail processing for iron parts?

In the machining industry, iron parts belong to common processing workpieces. When using machining centers to process iron parts, should we choose hard rail machining centers or wire rail machining centers?

When selecting hard rail machining center and wire rail machining center, machining manufacturers need to understand the size of iron parts processed by themselves, whether they are finish machining or rough machining,

Only by understanding these details can a manufacturer specializing in the production of CNC machining centers give an accurate answer.

Generally, large-size iron parts have high quality and large cutting amount. In this case, it is more appropriate to select the hard rail machining center. The hard rail machining center has strong rigidity, earthquake resistance and load-bearing capacity, which is more suitable for heavy-load cutting.

In this case, if the wire rail machining center is used for processing for a long time, the guide rail may be damaged. Customers are generally advised to use hard rail CNC machining centers, such as table group finishing machines T-8, T-10, T-12, T-13 and T-15, which are hard rail machining centers, compared with 850, 1060 and 1270 in the market. These hard rail CNC machining centers are generally suitable for heavy-duty cutting.

About CNC Turniing

ken. tang@chengcg.com

How to ensure the accuracy of CNC machining

For many non-standard parts processing customers, when selecting suppliers, they are most concerned about the machining accuracy of mechanical precision parts. In the precision machining industry, it is easy to find suppliers, but it is difficult to find CNC machining center suppliers with appropriate accuracy, so we must be cautious. In short, precision is risky and processing needs to be cautious.

Machining of mechanical precision parts

In the machining center of non-standard parts, more cutting tools are generally used in the machining process. In order to ensure the machining accuracy of precision parts, the replacement sequence of cutting tools must be arranged reasonably. The corresponding replacement of machining tools is the machining sequence. The general process principle is to make the datum first, then punch holes, and then divide the primary and secondary rough and then fine.

In the machining process of mechanical precision parts, the machining of datum surface is the best, which provides positioning reference for the machining of other surfaces. The benchmark of this process positioning is the benchmark of the next process positioning. Therefore, when the positioning datum of all processes of machining a non-standard part is determined, the sequence arrangement of the whole machining process can be pushed forward.

When arranging the processing sequence of mechanical precision parts, it must be clear whether non-standard parts need to be processed and processed. Pre machining is also usually done by CNC lathes. If the workpiece has high rough accuracy, the positioning is guaranteed, or the processing volume is sufficient, it can be processed directly in the machining center without pretreatment. This needs to consider the difference between the accuracy of the rough datum and the process of the machining center, which can be completed by several processes or one process.

Similarly, if the pretreatment surface has different standard requirements from the operation surface of the machining center, sufficient machining allowance must be reserved during pretreatment. At the end of one-time clamping in the machining center of non-standard mechanical precision parts, all machining contents including the pre machined surface must also be included to ensure the final machining accuracy of precision parts.

About CNC Turniing

ken. tang@chengcg.com

Influence of spindle speed on large CNC machining center

Since the development of large CNC machining centers, the total output value has gradually increased, and the domestic machine tool industry is becoming more and more prosperous. According to the appearance design of most machining centers in the market, the slicing conveyor can be adjusted to the back of the production line, which is suitable for customizing the arrangement of the production line, which is also one of the reasons why customers like it. The machine adopts high torque motor. The output of the motor can fully reflect the characteristics of the main shaft. The indexing disc has high efficiency and high precision, including 8 oil circuit joints. One air pressure is tightly confirmed and has high mobility. It can be used with oil pressure fixture.

The main shaft of the large NC machining center is a vertical machining center, the structural form is a fixed column, the worktable is rectangular and has no indexing rotation function. It is suitable for machining disc, sleeve and plate parts. It has three linear motion coordinate axes, and it can be installed on a rotary table rotating along the horizontal axis on the worktable to process spiral parts. The replacement of the machine tool adopts pneumatic mode, which is fast and convenient. The machine adopts automatic lubrication to ensure the good operation of all parts of the machine tool.

The structure of the machine tool adopts the form of horizontal carriage, and the layout is reasonable. The three-axis feed adopts precision ball screw connected with servo motor to improve the transmission accuracy. The X and y-axis guide rails of the machine adopt precision rolling linear guide rails with high feed sensitivity; The z-axis adopts rectangular hardened cast iron plastic sliding guide rail pair, which has good vibration absorption; The machine control system adopts AC servo system, which is suitable for the processing of complex parts, especially complex molds.

The machine tool spindle adopts servo spindle motor, and the spindle box is equipped with counterweight device to ensure the smooth operation of z-axis. As we all know, the spindle speed of large CNC machining center is generally high, but with the continuous improvement of spindle speed, especially the rapid and various random vibrations, the instability of rotating shaft will increase. When the anti fatigue strength of spindle is exceeded, the spindle rotation error will increase reversibly, and finally affect the machining accuracy of machine tool. Therefore, the selection of spindle speed is very important.

About CNC Turniing

ken. tang@chengcg.com

Skills of avoiding Tool Collision in CNC machining center

What are the tips for avoiding knife collision in CNC machining center? With the development of computer technology and the continuous expansion of CNC machining teaching, there are more and more NC machining simulation systems, and their functions are becoming more and more perfect. Therefore, it can be used in the preliminary inspection program to observe the movement of the tool to determine whether a collision may occur.

1、 Using the simulation display function of CNC machining center

Generally, advanced CNC machining centers have graphic display function. When inputting the program, you can call the graphic simulation display function to observe the tool path in detail, so as to check whether there is possible collision between the tool and the workpiece or fixture.

2、 Using the empty running function of CNC machining center

The idling function of CNC machining center can be used to check the correctness of tool path. When the program is in the NC machining center, you can install it on the tool or workpiece, and then press the empty operation button. At this time, the axis does not rotate, and the automatic operation is tracked according to the planned worksheet. At this time, you can find out whether the tool may contact the workpiece or fixture. However, in this case, it must be ensured that the tool cannot be installed when the workpiece is installed; When the tool is installed, the workpiece cannot be installed, otherwise collision will occur.

3、 Using the locking function of CNC machining center

General CNC machining center has locking function (full lock or single shaft lock). After entering the program, lock the z-axis, and you can use the coordinate value of the z-axis to judge whether there will be a collision. When applying this function, avoid tool change and other operations, otherwise the program cannot pass.

4、 Improve programming skills

Programming is the most important part of large CNC machining center. Improving programming skills can avoid some unnecessary collisions to a great extent.